Board machine and method of manufacturing a multilayer cardboard web

Abstract

A board machine and method for making a multilayer cardboard web, in which a first layer of the web having a printable surface is formed in a first forming unit and carried on an extended forming wire thereof through a couching unit where the first layer is couched with one or more additional layers, the multilayer web then being carried on the extended wire to a pick-up point. An upper press felt of a double-felted press picks up the web at the pick-up point such that the printable surface faces downward and contacts the lower press felt through the nip of the press. The lower felt is smoother than the upper felt, and the lower felt contacts the lower press roll for a minimum sector angle beyond an exit of the nip to ensure that the web follows the lower felt.

What is claimed is:  
     
       1. A board machine for making a multilayer cardboard web with a printable surface, comprising: 
       a wet section comprising a first forming unit for forming a first board layer on a forming wire, and at least one additional forming unit for forming at least one additional board layer and couching the first board layer with the additional board layer(s) to form the multilayer cardboard web; and  
       a press section comprising at least a first double-felted press that receives the multilayer web from the forming section, the first double-felted press being formed by an upper press member and a lower press member forming a nip therebetween, the lower press member comprising a press roll and being disposed within a loop of a lower press felt, the upper press member being disposed within a loop of an upper press felt, the upper and lower press felts passing through the nip with the multilayer web sandwiched therebetween;  
       wherein the forming and press sections are structured and arranged such that the printable surface is formed on the first board layer and the forming wire of the first forming unit carries the multilayer web up to the double-felted press, the upper press felt picks up the multilayer web from the forming wire such that the printable surface faces downward and contacts the lower press felt as the multilayer web passes through the nip, and the lower press felt has a smoother web-contacting surface than that of the upper press felt so as to exert a greater adhesion force on the multilayer web.  
     
     
       2. The board machine of  claim 1 , wherein the upper press member includes a shoe defining a surface that faces the press roll, and at a discharge side of the nip the lower press felt remains in contact with the press roll for a sector angle α of at least 10° beyond a 0 point at which the surface of the shoe transitions from a concave to a convex curvature. 
     
     
       3. The board machine of  claim 2 , wherein the upper press felt departs the nip at an angle β relative to a 0 line that is tangent to the shoe at said 0 point, the angle β being about −5° to +5°. 
     
     
       4. The board machine of  claim 2 , wherein the upper press member comprises a shoe roll including said shoe. 
     
     
       5. The board machine of  claim 1 , wherein the upper press member comprises a press roll having an outer surface that is tangent to the lower press member at a 0 point, and at a discharge side of the nip the lower press felt remains in contact with the lower press roll for a sector angle α of at least 10° beyond the 0 point. 
     
     
       6. The board machine of  claim 5 , wherein the upper press felt departs the nip at an angle β relative to a 0 line that is tangent to the lower press roll at said 0 point, the angle β being about −5° to +10°. 
     
     
       7. The board machine of  claim 1 , wherein the press section includes a second double-felted press. 
     
     
       8. The board machine of  claim 7 , wherein each double-felted press comprises a shoe press in which the upper press member includes a press shoe. 
     
     
       9. The board machine of  claim 8 , wherein each upper press member comprises a shoe roll. 
     
     
       10. The board machine of  claim 7 , wherein the second double-felted press is arranged such that the upper press felt thereof picks the multilayer web up from the lower press felt of the first double-felted press. 
     
     
       11. The board machine of  claim 8 , wherein each double-felted press comprises a roll press in which the upper press member comprises a press roll. 
     
     
       12. A method for manufacturing a multilayer cardboard web with a printable surface, comprising: 
       forming a first board layer in a first forming unit such that the first board layer has said printable surface;  
       forming at least one additional board layer in at least one additional forming unit;  
       couching the first board layer and said at least one additional board layer together to form a multilayer cardboard web having said printable surface;  
       transferring the multilayer cardboard web onto a lower press felt of a first double-felted press with said printable surface in contact with a surface of the lower press felt, wherein the first double-felted press comprises an upper press member disposed within a loop formed by an upper press felt and a lower press member disposed within a loop formed by the lower press felt; and  
       passing the multilayer cardboard web through a nip of the first double-felted press sandwiched between the lower press felt and the upper press felt;  
       wherein the surface of the lower press felt in contact with the printable surface of the multilayer cardboard web is smoother than a web-contacting surface of the upper press felt in contact with an opposite surface of the web so as to cause the web to remain adhered to the lower press felt as the press felts diverge downstream of the nip.  
     
     
       13. The method of  claim 12 , wherein the upper press member includes a shoe and the lower press member comprises a press roll, the shoe defining a surface that forms an extended nip with the press roll, and wherein at a discharge side of the nip the lower press felt remains in contact with the press roll for a sector angle α of at least 10° beyond a 0 point at which the surface of the shoe transitions from a concave to a convex curvature. 
     
     
       14. The method of  claim 13 , wherein the upper press felt departs the nip at an angle β relative to a 0 line that is tangent to the shoe at said 0 point, the angle β being about −5° to +5°. 
     
     
       15. The method of  claim 12 , wherein the upper press member comprises a press roll having an outer surface that is tangent to the lower press member at a 0 point, and at a discharge side of the nip the lower press felt remains in contact with the lower press roll for a sector angle α of at least 10° beyond the 0 point. 
     
     
       16. The method of  claim 15 , wherein the upper press felt departs the nip at an angle β relative to a 0 line that is tangent to the lower press roll at said 0 point, the angle β being about −5° to +10°. 
     
     
       17. The method of  claim 12 , wherein the multilayer cardboard web is dewatered by passing the web through the first double-felted press and then through a second double-felted press, the upper press felt of each press receiving the web upstream of the nip. 
     
     
       18. The method of  claim 17 , wherein the upper press felt of the first double-felted press picks the multilayer cardboard web up from an extended forming wire of the first forming unit, and the upper press felt of the second double-felted press picks the web up from the lower press felt of the first double-felted press after the web has passed through the first double-felted press.